The nephrin gene (or NPHS1) was positionally cloned from chromosome 19q13 as the causative gene for Finnish-type congital nephrotic syndrome (FtCNS). Thus effort has provided a superb opportunity to elucidate the molecular pathogenesis of glomerular proteinuria becuase the nephrin protein is a critical component of the glomerular slit diaphragm, which normally prevents glomerular protein leakage. In some FtCNS cases, nephrin promoter mutations indicate that the gene may be abnormally regulated at the transcriptional level. Nephrin is also likely involved in more common causes of the nephrotic syndrome. Intriguingly, neprin is expressed almost exclusively in mature glomerular podocytes. We plan to use the nephrin genomic locus as a tool to determine what DNA elements, and ultimately what corresponding transfactors, might permit podocyte-specific nephrin expression. Our Aims are as follows: 1. Identify a nephrin genomic DNA fragment that confers podocyte-specific expression to a reporter gene. 2. Determine whether nephrin promoter mutations affect nephrin expression. 2 (alternative). Determine the effects of WT1 splice variants and WT1 mutations n nephrin expression. These studies will allow us to identify DNA elements that permit genes to be expressed exclusively in podocytes, which will be useful for in vivo studies of podocyte biology and perhaps for gene therapy. More importantly, this effort will ultimately help identify tranfactors and signaling pathway components that control podocyte differentiation that might even be encoded by new nephrotic syndrome genes.